This invention relates to a shoe sole having a midsole formed of several layers, particularly a sole of the type used for running shoes, particularly for medium and long distance running.
In the case of soles of this type, the midsole usually is formed of a material that is more elastic than that of the outer sole, preferably of a plastic foam material, foam rubber or a similar material. It is also known to develop the midsole so that it rises toward the rear in a wedge-shaped manner and to compose it of several layers. An example of such a sole can be found in U.S. Pat. No. 4,237,627.
It is a primary object of this invention to construct a shoe sole having a midsole of the initially mentioned type for athletic shoes, especially for the running disciplines, in such a way that the distribution of stress occurring during running and affecting the foot and the joints, especially the ankle and the arch of the foot, is controlled in such a way that injuries, especially injuries to the ankle, and premature fatiguing are largely avoided or even prevented. In particular, it is a particular object for a sole with a midsole is to be developed that will counteract the lateral stresses occurring during running, known as "pronation," and which twist the foot.
In this connection, it is known to incorporate a material of greater hardness and lesser resiliency into the midsole of a running shoe at the inner, medial, side in the area of the heel in order to act as a heel stabilizer that will counteract pronation. Examples of soles incorporating such stabilizing portions into the midsole can be found in U.S. Pat. Nos. 4,364,188 and 4,364,189, as well as co-pending, commonly assigned U.S. application Ser. No. 387,667, filed June 11, 1982. However, such prior art midsoles often have a somewhat patch-work external appearance and can be subject to problems resulting from penetration of wetness, particles or other substances between layers or sections. Furthermore, manufacture of such compound midsoles can be complicated and expensive, and from a practical standpoint, places limitations on the configurations which can be used for the respective portions of the midsole.
Thus, it is a further object of the present invention to provide a shoe sole having a midsole which would avoid problems of wetness, particles and other substances penetrating into the midsole and, also, would provide greater freedom to configure the various portions of different materials in optimal fashion.
In order to achieve the above-noted objects, the sole in accordance with the present invention has a midsole with a softly elastic inner part, which extends from the toe area to the heel, a hard elastic stabilizer, which is located under the softly elastic inner midsole part in a portion of the heel area, and a cushioning piece of softly elastic material, which underlies the inner midsole part in the portion of the heel area not occupied by the stabilizer. Furthermore, the unit comprised of the inner midsole part, stabilizer and cushioning piece is surrounded by a softly elastic sheathing that, advantageously, is injection-molded or cast about the unit.
By means of the softly elastic sheathing of the individual parts of the midsole, a cohesive midsole is formed which ensures its individual elements are effectively held together and may, especially, also be shaped according to the bed of the foot. The stabilizer, that may be C-shaped, L-shaped or I-shaped, counteracts the above-mentioned "pronation," while the cushioning piece absorbs the pressure affecting the heel when the foot impacts. This cushioning piece, in particular, has good spring-back characteristics so that the compression energy can be used for absorbing shocks and, therefore, makes possible an increase in performance of the athlete wearing this type of shoe. By means of the combination of these three inside elements, extremely good stability is achieved which also prevents a twisting of the rear part of the foot without impairing the required damping of pressure and rolling-off characteristics. The sheathing, finally, also causes an additional absorption of shocks while durably and firmly enclosing the individual elements. It is also useful for keeping out wetness and prevents penetration of particles or substances into the midsole that can have an eroding effect.
Furthermore, because a sheathing is molded or cast about individual formed elements to hold them together, complicated interfitting shapes can be used since relatively simple molds and molding apparatus can be used to form each element and to form the sheathed unit.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention